Acids

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Acids Bases

• Calculating Ka from Dissociation
• Polyprotic Acids
• Properties of Salts

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Example

• Lactic acid (HC3H5O3) is a waste product that
  accumulates in the muscle during exertion,
  leading to pain a feeling of fatigue. A 0.100 M
  solution is 3.7 dissociated. Calculate Ka.

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Example
HC3H5O3 ? H C3H5O3 -
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Polyprotic Acids

• More that one ionizable H
• H come off one at a time
• Each one has a specific Ka value
• Ka1gtgtgtgtKa2gtgtKa3
• When calculating the pH of a polyprotic acid, you
  only use the 1st Ka because all of the others are
  so small

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Complete Ionization

• Write the steps for the complete ionization of
  H2Se

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Complete Ionization

• Write the steps for the complete ionization of
  H3AsO

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Example

• Calculate the pH the of all species of a
  3.0 M solution of H3PO4.
• Ka1 7.5 x 10-3, Ka2 6.2 x 10-8, Ka3 4.8 x
  10 -13

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Example
H3PO4 ? H H2PO4-
Ka1 7.5 x 10-3
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Example
H2PO4 - ? H HPO4-2
Ka1 6.2 x 10-8
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Example
HPO4 -2 ? H PO4-3
Ka3 4.8 x 10-13
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Example

• pH
• H3PO4
• H2PO4-
• HPO4-2
• PO4-3
• H

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Acid Base Properties of Salts

• Salts of weak acids produce basic solutions
• NaC2H3O2

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Acid Base Properties of Salts

• Salts of weak bases produce acidic solutions
• NH4Cl

14
Acid Base Properties of Salts

• Salts of strong acids Bases produce neutral
  solutions
• NaCl

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Calculations with salts

• KaxKb Kw
• Can find Ka or Kb with this equation
• On AP formula sheet

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Example

• What is the pH if a 0.140M solution of NaC2H3O2
  (Ka HC2H3O2 1.8x10-5)

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Another example

• What is the pH of a 0.140M solution of
  diethylaminochloride (C2H5)2NH3Cl.
• Kb (C2H5)2NH3 1.3x10-3
• (C2H5)2NH3Cl ? (C2H5)2NH3 Cl-
• (C2H5)2NH3 H2O ? (C2H5)2NH2 H3O

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Qualitative Predictions of pH

• KagtKb ? acidic
• KbgtKa ? basic
• Ka Kb ? neutral

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pH Predictions

• Predict if an aqueous solution of the following
  are acidic, basic, or neutral
• NH4C2H3O2
• Kb NH4 1.8x10-5
• Ka HC2H3O2 1.8x10-5

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pH Predictions

• Predict if an aqueous solution of the following
  are acidic, basic, or neutral
• NH4CN
• Kb NH4 1.8x10-5
• Ka HCN 6.2x10-10

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Effect of Structure of Acid Base Properties

• Weak acid (HF)
• Stays together
• Strong acids
• Look at electronegativity

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Effect of Structure of Acid Base Properties